1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a resin structure reinforced with long fibers. More particularly, the invention relates to an apparatus and a method for manufacturing a resin structure reinforced with long fibers in which a continuous fiber bundle impregnated with a resin melt is moved while being supported in grooves provided in the outer periphery of a plurality of upper and lower rolls arranged in an alternating manner, thereby shaping the fiber bundle.
2. Background of the Invention
Resin structures reinforced with long fibers in which thermoplastic resins are reinforced with continuous fibers have become of much interest in recent years, since they have physical characteristics much superior to those reinforced with short fibers. They are generally manufactured by a so-called pultrusion method in which a continuous reinforcing fiber bundle is impregnated with a thermoplastic resin while drawing the fiber bundle through a cross-head extruder and then pulled through a die (U.S. Pat. No. 3,993,726), or a continuous reinforcing fiber bundle is immersed in a thermoplastic resin melt to wet it while it is drawn and then pulled through a die (Japanese Patent Application Laid-open (kokai) No. 57-181852). In either case, the resulting reinforced resin structure is cut to an arbitrary size and used. Pellets obtained by the above methods are not only easily processed into articles with an intended shape by known means such as injection molding, extrusion molding, or compression molding, but also have excellent physical characteristics, and therefore, they are receiving much industrial attention.
FIG. 6 shows an example of a conventional apparatus or method for manufacturing a resin structure reinforced with long fibers with a pellet shape. In FIG. 6, 1 is a fiber bundle taken out of a roving, 2 is a roll bar, 3 is an extruder from which a thermoplastic resin melt is supplied, 4 is a cross-head die for impregnating the fiber bundle 1 with a thermoplastic resin melt, 5 is a fiber bundle impregnated with a thermoplastic resin melt, 6 is a shaping die, 7 is a take-up roll, and 8 is a pelletizer which functions as a cutting means. The shaping die has a through hole through which passes a continuous fiber bundle 5 impregnated with a thermoplastic resin melt at the cross-head die 4. By changing the configuration of the through hole, the cross section of the resulting pellet-shaped resin structure reinforced with long fibers can be varied to have an intended shape.
That is, when a continuous fiber bundle 5 impregnated with a thermoplastic resin melt at the cross-head die 4 passes through the shaping die 6, it is shaped to have a desired shape such as a strand, rod, ribbon, tape, sheet, plate, or any other special shape, and at the same time, the fiber bundle is uniformly impregnated with the thermoplastic resin and the impregnation is accelerated. The continuous fiber bundle impregnated with a resin melt 5 is taken up with a take-up roll 7 after passing through the shaping die 6. The resin structure reinforced with long fibers which has been taken up is cut to an arbitrary length with cutting means 8. The cut resin structure is then shaped or submitted to other processes. The thus-obtained resin structure reinforced with long fibers contains reinforcing fibers which have substantially the same length as the resin structure and which are aligned in parallel to the longitudinal direction of the resin structure.
Conventional apparatuses and methods for manufacturing a resin structure reinforced with long fibers involve the drawback that the resulting resin structure (for example, a pellet) tends to have poor quality, that is, it often causes cracks or fibers are separated, since the cross section of the resin structure is shaped only with a shaping die. In detail, a continuous fiber bundle impregnated with a resin melt 5 is shaped by the shaping die as the fiber bundle moves through a through hole having a cross section corresponding to that of the target product. Therefore, when a fiber bundle is impregnated with a resin melt unevenly in cross section, only the resin-rich side is chipped off and shaped, leaving a concavity which is attributed to the shortage of a resin melt at the opposite side. As a result, it sometimes happens that the intended shape, for example, a columnar shape (in this case, the cross section is a circle) of the target resin structure becomes a macaroni-like shape or flattened shape.
In addition, use of a shaping die causes other problems in which, especially in the manufacture of products with a natural color, the resin undergoes a prolonged thermal hysteresis during its stay in the die, which causes burning or discoloring (or fading) and in addition formation of carbide contaminants.
The present invention was accomplished in view of the foregoing situation.